The present invention is broadly directed to a glide head structure adapted for use with a system for testing moving surfaces to detect a presence of asperities thereon. More particularly, the present invention is directed to a glide head assembly that is adapted to detect asperities which project a specified height above moving surfaces. Even more specifically, the present invention concerns a glide head assembly that is adapted to generate an electronic signal in response to the presence of an asperity located on a surface of a rigid memory disk, and a test device incorporating the same.
In recent years, perhaps the most revolutionary development in the history of technology has been the computer. While the fundamental components of a computer""s architecture remain the same, the capabilities of these individual components have increased exponentially as technology rapidly progresses. Common to almost every computer is a processing unit which receives input information and processes this information to generate an output. A computer program instructs the processing unit to perform various tasks, and an associated memory unit is incorporated to store instructions for the processing unit and to hold temporary results that occur during operation. The potential applications for computers are virtually limitless and ongoing efforts are made to design computers which are capable of carrying out these repetitious and complex operations at faster speeds.
Computer memories are used to store or xe2x80x9crememberxe2x80x9d a system of on-off codes for access at a later time, and systems accomplish this in a variety of ways, such as through the utilization of magnetic disks, microchips or optical devices. Where magnetic disks are concerned, patterns of magnetism are formed on the disks in order to store desired information. A magnetic disk may be in the form of either a floppy disk which is used to store and retrieve programs and data, or an arrangement of hard disks which are permanently enclosed in a hard disk drive to prevent contamination. Hard disks have a much greater memory capacity than floppy disks. Memory capacity, of course, is measured in kilobytes, megabytes or even gigabytes, with a single byte equal to eight bits of a binary code.
The hard disk drive for rigid, magnetic memory disks is akin to a conventional record turntable in that a mechanism rotates the disk with a selected angular velocity and translates a magnetic read-write head across the disk surface to permit a selected annular track to be accessed. The magnetic disks are typically journaled for rotation about a spindle in a spaced relationship to one another. A tracking arm is associated with each disk and the read-write head is mounted to this tracking arm for accessing the desired information. Conventional magnetic heads are typically referred to as xe2x80x9cflyingxe2x80x9d data heads because they currently are constructed not to contact the surface of the disk during rotation. Rather, these heads hover above the surface on an air bearing that is located between the disk and the head and which is caused, at least in part, by rotation of the disk at high speeds.
A persisting problem with rigid magnetic memory disks is that asperities, i.e., protrusions on the surfaces of the disks, may cause an anomaly when encountered by the read-write head during high speed revolutions. These asperities can cause errors in the transfer of information or even damage to the read/write head. In an effort to reduce the occurrences of asperities, manufacturers commonly burnish the surfaces of disks. In the burnishing process a burnishing head, rather than a magnetic read-write head, is mounted in a similar manner relative to the disk as discussed above. During the burnishing process, the burnishing head operates to smooth out these surface protrusions.
The next step in further refining magnetic disks for production is through the use of a glide head. The purpose of a glide head is to detect, via proximity or contact, any asperities remaining after the burnishing operation which may come into contact with the data head during use. Glide heads are required to hover and detect asperities which are located above specified data head flying heights. Glide heads thus dynamically test the integrity of a disk""s surfaces.
The magnetic media industry, in particular, is requiring that magnetic disks have increasing recording densities. Accordingly, for manufacturers to develop production quality rigid memory disks for use in this industry and the computer industry in general, it is necessary to utilize glide heads having more sensitive response characteristics. Existing glide heads have inherent problems because it is difficult to precisely control the electrical response characteristics of these devices.
The electrical response of a glide head is dependent upon detection parameters such as amplitude, frequency, and signal to noise ratio (SIN). However, because the industry""s demands for higher magnetic densities require a lowering of the data heads"" flying height over the surface of the magnetic disks, it becomes more difficult to tighten the physical tolerances of glide heads and effectively control these parameters.
In the past it has been known to employ a glide head assembly whose slider component is configured to include a lateral wing portion that has a layer of piezoelectric material adhered on an upper surface thereof. This piezoelectric material is approximately 20-30 mls (0.020-0.030 inches) thick. As the slider contacts a surface asperity, the crystalline lattice of the piezoelectric material is disturbed. This disturbance causes an electronic signal to be sent, via electrical lead wires, to a signal processing unit. Unfortunately, the same disturbances also causes a variety of other electronic signals to be sent to the processing unit. These other signals are caused by resonant vibrations of other components in the glide head assembly, as well as inherent noise in the system. The frequencies of these mixed electronic signals are unpredictable and, therefore, it is difficult to adequately filter that electronic signal which is specifically associated with the encountered asperity. It is, therefore, difficult with these prior devices to reliably detect the presence of asperities on the surfaces of rigid memory disk.
Accordingly, there remains a need to provide a new and useful glide head assembly which has more reliable electrical response characteristics during the asperity detection process. The present invention is directed to meeting this need.
It is an object of the present invention to provide a new and useful glide head assembly, that is adapted for use with a test system for detecting a presence of asperities on a moving surface.
Another object of the present invention is to provide a new and useful test device for testing the surface of a rotating disk to determine a presence of asperities thereon.
A further object of the present invention is to provide a new and useful glide head assembly which exhibits improved electrical response characteristics during the asperity detection process.
Still a further object of the present invention is to provide a glide head structure adapted to mount to a flexure for use with a test system for detecting a presence of asperities on a moving surface.
In furtherance with these objectives, the present invention is directed to a glide head assembly that is associated with a mounting structure and adapted for use with a test system for detecting a presence of asperities on a moving surface, preferably that of a rigid memory disk. The test system includes a signal processor operative to process an electronic signal that is generated in response to the presence of the asperity.
Broadly, the glide head assembly of the present invention comprises an elongated flexure having a longitudinal axis and including a first end portion attachable to the mounting structure and a second end portion opposite the first end portion. This second end portion is adapted to be positioned in proximity to the moving surface when in an operative state. A slider is disposed on the second end portion and this slider has a first surface facing the moving surface when in the operative state and a second surface opposite the first surface. A surrounding sidewall surface extends between the slider""s first and second surfaces. A piezoelectric transducer is supported on the sidewall surface and projects outwardly therefrom. The slider is secured to the flexure""s second end portion by a first layer of first adhesive and the piezoelectric transducer is secured to the sidewall surface by a second layer of second adhesive. This transducer is responsive in the operative state to the presence of an asperity relative to the slider as the asperity moves past the slider to vibrate, thereby to produce the electronic signal at a selected signal frequency.
The piezoelectric transducer is elongated along a central transducer axis and is mounted to a face of the surrounding sidewall surface that extends transversely to the longitudinal axis. A proximal end of the transducer is mounted to this face and projects outwardly therefrom to terminate at a free distal end. Preferably, the piezoelectric transducer extends forwardly of the flexure""s second end portion and has a reduced thickness relative to the slider. Further, the piezoelectric transducer may include a proximal end mounted to the slider and a pair of legs extending longitudinally from the proximal end to terminate, respectively, at first and second free distal ends. The pair of legs define first and second leg portions.
The present invention also relates to a test device for testing opposed moving surfaces of a rotating memory disk to determine a presence of asperities thereon. This test device comprises a mounting structure, a rotary drive operative to rotate the memory disk relative to the mounting structure, at least a first glide head assembly supported on the mounting structure, a signal processor and electrical interconnects. The first glide head assembly is preferably constructed as discussed above so that it includes a flexure, a slider and a piezoelectric transducer that is responsive in an operative state to the presence of an asperity to produce an electronic signal at a selected signal frequency. As such, the electrical interconnects are employed to establish electrical communication between the piezoelectric transducer and the signal processor which operates to process this electronic signal. A glide head structure is also provided which comprises a slider and a piezoelectric transducer, each as described above.